PSI - Issue 44

Flora Faleschini et al. / Procedia Structural Integrity 44 (2023) 1616–1623 Flora Faleschini et al. / Structural Integrity Procedia 00 (2022) 000–000

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4.1. Seismic hazard analysis The so-called Probabilistic Seismic Hazard Analysis for the computation of #$ associates to each value, the annual rate of events that exceed it at a given site. The seismicity of a given area di defined by three main components: the earthquake occurrence model, the spatial seismogenic model and the attenuation model. | 01 | represents the mean number of events per year with an intesity of exactly im and is obtained as: | 01 | = − 34 56 3(#$) ( ) (2) On the other hand, #$ is obtained via the following PSHA integral: #$ = ∑ $ ;<=,< ∫ ∫ [ > | , ] C < ( ) D < ( ) F ;GH,< F ;<=,< $ ;GH,< $ ;<=,< I JK #LM (3) where $ ;<=,< is the rate of occurrence of earthquakes greater than a suitable minimum magnitude $#I,# of the i th seismogenic zone, C < ( ) is the magnitude distribution for the i th seismogenic zone and D < ( ) is the distribution of the source i th -to-site distance. Given a combination of magnitude m and distance r , [ > | , ] is the probability to exceed . The seismic hazard map for Italy is provided by the National Institute of Geology and Volcanology (INGV). To compute the failure rate a continuous hazard function is needed. Since hazard data bu INGV (values of the 16 th , 50 th and 84 th percentile) are provided only for nine return times, it is possible to fit the median values (i.e., the 50 th percentile) with a quadratic function in the logarithmic space as: ( ) = P (RS T UV(W)RS X YI X (W)) (4) In assessing seismic reliability, instead of the median hazard curve, it is more suitable to refer to the mean one which is possible to derive with the following equation: ̅( ) = ( ) ( T X [ \X ) (5) where ^ can be estimated as: ^ = UV(_ `a% )RUV(_ Tc% ) d (6)

Figure 2: Interpolation of the seismic hazard curve in the considered site.